1. Field of the Invention
The invention relates to a rotor for a rotary electric machine, and more particularly to a rotor for a rotary electric machine in which a plurality of magnetic poles are disposed at intervals, in a circumferential direction, at an outer periphery of a rotor core.
2. Description of Related Art
For example, Japanese Patent Application Publication No. 2001-45283 (JP-A-2001-145283) discloses a conventional rotor 60 of a permanent magnet-type rotary electric machine in which a plurality of magnetic poles 62 having a configuration such as the one illustrated in FIG. 6 are provided, at equal intervals, in the circumferential direction of a rotor core 64. The magnetic poles 62 of the rotor 60 are made up of four permanent magnets 66, 68a, 68b, 70.
The four permanent magnets are disposed so as to form a quadrangle, more specifically a trapezoid, in a cross section of the rotor core 64. Specifically, a first permanent magnet 66 is disposed at an outer periphery of a rotor core 64, in the center of the magnetic pole 62 in the circumferential direction. Second permanent magnets 68a, 68b are disposed, substantially along radial direction, on both sides of the first permanent magnet 66, at positions spaced apart from each other in the circumferential direction. A third permanent magnet 70 is disposed on an inner periphery side in the radial direction of the rotor core 64, facing in the direction of the first permanent magnet 66.
The first permanent magnet 66 is disposed in a main portion 74a of a magnet groove 74 that is formed, extending in the axial direction, in the rotor core 64. The magnet groove 74 has sub-portions 74b, 74c on both sides of the main portion 74a, in the circumferential direction, such that the sub-portions 74b, 74c communicate with the main portion 74a. Leading end portions 74x, 74y of the sub-portions 74b, 74c of the magnet groove 74 are formed so as to project towards the outer periphery. The second permanent magnets 68a, 68b are respectively disposed inside main portions 76a of magnet grooves 76 that are formed, extending in the axial direction, in the rotor core 64. The magnet grooves 76 include respective sub-portions 76b that extend outward in the radial direction of the abovementioned main portions 76a. 
In the magnetic pole 62 of the rotor 60, a core region is formed, as a magnetic path central portion 72, between the first permanent magnet 66 and the third permanent magnet 70. Magnetic path entrance portions 73 are formed between the sub-portions 74b, 74c of the magnet groove 74, the second permanent magnets 68a, 68b, and the sub-portions 76b of the magnet groove 76. The magnetic path central portion 72 is linked to the outer peripheral face of the rotor core 64 via the magnetic path entrance portions 73 on both sides of the first permanent magnet 66 in the circumferential direction. The two magnetic path entrance portions 73 on both sides of the first permanent magnet 66 in the circumferential direction cause magnetic flux from the stator (not shown) that penetrates into the rotor core 64 to be drawn from one of the magnetic path entrance portions 73 out through the other, through the magnetic path central portion 72. In the case of a reversed flow direction of the magnetic flux, however, the inlet and outlet of magnetic flux are reversed, and hence both portions are referred to as magnetic path entrance portions.
Herein, JP-A-2001-145283 indicates that in the rotor 60 having a magnetic pole 62 configured as described above, no magnetic flux is received, in the reverse direction of the magnetization direction, at both end portions of the first permanent magnet 66 in the circumferential direction, by virtue of the presence of the sub-portions 74b, 74c, which include voids (or a resin) of lower permeability than that of the core material, on both sides of the first permanent magnet 66. As a result, degaussing does not occur in the first permanent magnet 66.
In the rotor 60 of JP-A-2001-145283, the sub-portions 74b, 74c of the magnet groove 74 are disposed parallel to the second permanent magnet 68a, 68b and the sub-portions 76b of the magnet groove 76, and the magnetic path entrance portions 73 formed therebetween have constant width. In this case, the magnetic flux leaking from the circumferential-direction end portion of the first permanent magnet 66 and the magnetic flux from the second permanent magnets 68a, 68b concentrate at the inner-periphery-side portion of the magnetic path entrance portion 73 when there increases the amount of magnetic flux that flows from the stator during high load operation of the rotary electric machine that is provided with a rotor 60. The q-axis inductance Lq of the magnetic pole 60 may drop significantly as a result, and, in consequence, reluctance torque during high load operation may be harder to obtain, and torque generation efficiency may drop accordingly.
Herein, d-axis inductance Ld is predominant, upon high load operation of the rotary electric machine, in the reluctance torque, which increases proportionally to the difference between the q-axis inductance Lq and the d-axis inductance Ld. Accordingly, there is room for improvement regarding this feature.